Neural stem cells are useful as donor cells in transplant therapies for treating neurological disorders such as a spinal cord injury, and are anticipated for applications in regenerative medicine (Okano H, Ogawa Y, Nakamura M, kaneko S, Iwanami A, Toyama Y. (2003). “Transplantation of neural stem cells into the spinal cord after injury”. Seminars in Cell & Developmental Biology 14(3): 191-198.). While it is known that the neural stem cells can be produced from embryonic stem cells (ES cells) (Okada Y, Matsumoto A, Shimazaki T, Enoki R, Koizumi A, Ishii S, Itoyama Y, Sobue G, Okano H. Stem Cells. 2008 Dec.;26(12):3086-98. Epub 2008 Aug. 28.), the use of human ES cells has been at issue from ethical viewpoints.
Recently, it became possible to produce induced pluripotent stem cells (iPS cells) having a pluripotency similar to the ES cells by selecting cells expressing Fbx15 gene among the cells which are obtained by introducing Oct3/4 gene, Sox2 gene, Klf4 gene and c-myc gene into somatic cells such as fibroblasts or hepatocytes and allowing them to grow (Takahashi K, Yamanaka S. (2006). “Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors.”. Cell 126: 663-676; Takahashi K, Okita K, Nakagawa M, Yamanaka S. (2007). “Induction of pluripotent stem cells from fibroblast cultures”. Nature Protocols 2: 3081-3089; Aoi T, Yae K, Nakagawa M, Ichisaka T, Okita K, Takahashi K, Chiba T, Yamanaka S. (2008). “Generation of pluripotent stem cells from adult mouse liver and stomach cells”. Science 321(5889): 699-702; International Patent Publication WO2007/069666). The iPS cells have several advantages: for example, they are less ethically problematic because they can be established without using an embryo but rather with using somatic cells and rejection can be avoided when used in transplantation because they can be established from the cells of the recipient himself. Therefore, the neural stem cells produced by using the iPS cells would be more useful than the ES cells.